A light emitting diode (LED) is a semiconductor light source which is often used as an indicator lamp. Early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness. An LED is often small in area (e.g., less than 1 square millimeter), and an optical device usually comprises the LED as a lighting source and integrated optical components to shape its radiation patterns.
As for the optical device, the LED as a form of a chip is often secured onto a substrate and positioned in the recess of a bowl-shaped collimator lens. The lens is rotationally symmetrical in shape and has an associated axis of symmetry. The position of the LED and the shape of the lens are attuned to each other in such a manner that a large part of the light generated by the LED is converted through refraction and reflection into a parallel light beam which leaves the lens.